849 research outputs found
Current issues relating to artificial reefs in European seas
European artificial reef research has now been active for about three decades. For much of that time research has been conducted within national programmes, focussing on national or local issues, and has taken place predominately in the Mediterranean Sea. Over the past ten years or so interest in artificial reef technology and science has spread into the NE Atlantic and Baltic Sea with an associated variation in aims and ideas. Reef scientists working in European seas have run projects to assess artificial reefs as tools to protect habitat from destruction from trawling (Spain, Italy and France), promote nature conservation (Monaco, Italy and France), aid fisheries (Italy, Spain, Portugal and France), assess novel materials for reef construction (Italy and UK), investigate habitat use for lobsters (UK, Italy and Israel), for aquaculture (Italy), as experimental sites where habitat parameters are known (UK, Holland and Italy) and as biofiltration structures (Finland, Russia, Poland and Romania). This variety of investigation is one of the strengths of artificial reef research in Europe, the community is diverse and there is great scientific value in establishing collaboration and dialogue with colleagues.
The majority of artificial reef investigations have been, and still are, experimental with Italy dominating the research effort and Spain currently leading the way in the tonnage of reef material deployed, primarily for seagrass habitat protection. Problems associated with old descriptive, qualitative research have led to developments in quantification and comparative studies which have allowed a scientific perspective to be put on artificial reef deployments across Europe. Currently, as part of the EARRN (European Artificial Reef Research Network) initiative, there is an acceptance of the need to standardise some of the ecological methods used. If this is not practicable in some cases then at least the reporting of results will be done in such a way to allow comparison with data gathered elsewhere
Gauge Theories on a 2+2 Anisotropic Lattice
The implementation of gauge theories on a four-dimensional anisotropic
lattice with two distinct lattice spacings is discussed, with special attention
to the case where two axes are finely and two axes are coarsely discretized.
Feynman rules for the Wilson gauge action are derived and the renormalizability
of the theory and the recovery of the continuum limit are analyzed. The
calculation of the gluon propagator and the restoration of Lorentz invariance
in on-shell states is presented to one-loop order in lattice perturbation
theory for on both 2+2 and 3+1 lattices.Comment: 27 pages, uses feynmf. Font compatibility adjuste
Initial-State Interactions in the Unpolarized Drell-Yan Process
We show that initial-state interactions contribute to the
distribution in unpolarized Drell-Yan lepton pair production and , without suppression. The asymmetry is expressed as a
product of chiral-odd distributions , where the quark-transversity function
is the transverse momentum dependent, light-cone
momentum distribution of transversely polarized quarks in an {\it unpolarized}
proton. We compute this (naive) -odd and chiral-odd distribution function
and the resulting asymmetry explicitly in a quark-scalar diquark
model for the proton with initial-state gluon interaction. In this model the
function equals the -odd (chiral-even) Sivers
effect function . This suggests that the
single-spin asymmetries in the SIDIS and the Drell-Yan process are closely
related to the asymmetry of the unpolarized Drell-Yan process,
since all can arise from the same underlying mechanism. This provides new
insight regarding the role of quark and gluon orbital angular momentum as well
as that of initial- and final-state gluon exchange interactions in hard QCD
processes.Comment: 22 pages, 6 figure
Deeply Virtual Neutrino Scattering (DVNS)
We introduce the study of neutrino scattering off protons in the deeply
virtual kinematics, which describes under a unified formalism elastic and deep
inelastic neutrino scattering. A real final state photon and a recoiling
nucleon are detected in the few GeV ( GeV) region of momentum
transfer. This is performed via an extension of the notion of deeply virtual
Compton scattering, or DVCS, to the case of a neutral current exchange. The
relevance of this process and of other similar exclusive processes for the
study of neutrino interactions in neutrino factories for GeV neutrinos is
pointed out.Comment: 28 pages, 12 figures, revised final version, to appear in JHE
Generalized parton distributions and Deeply Virtual Compton Scattering in Color Glass Condensate model
Within the framework of the Color Glass Condensate model, we evaluate quark
and gluon Generalized Parton Distributions (GPDs) and the cross section of
Deeply Virtual Compton Scattering (DVCS) in the small- region. We
demonstrate that the DVCS cross section becomes independent of energy in the
limit of very small , which clearly indicates saturation of the DVCS
cross section. Our predictions for the GPDs and the DVCS cross section at
high-energies can be tested at the future Electron-Ion Collider and in
ultra-peripheral nucleus-nucleus collisions at the LHC.Comment: 20 pages, 8 Figure
Formation and Evolution of Quark-Gluon Plasma at RHIC and LHC
Initial conditions for quark-gluon plasma formation at \tau=0.1\fm are
considered in lowest order perturbative QCD. Chemical composition,
thermalization of the formed semihard quark-gluon system and especially
implications of the new HERA parton distributions with the enhancement at small
are studied. The plasma at \tau=0.1\fm is shown to be strongly gluon
dominated both at RHIC and LHC, and a possibility for rapid thermalization of
gluons at LHC is pointed out. Uncertainties in the calculations, particularly
shadowing corrections to the parton distributions, are discussed. Free
streaming and ideal hydro limits for the evolution of the gluonic plasma with
the calculated minijet initial conditions are demonstrated, and a lower limit
for final multiplicities obtained for the LHC nuclear collisions.Comment: the uuencoded ps-file is replaced by the tex-file and a separate
uuencoded file for the figures
Adaptive dynamic control of quadrupedal robotic gaits with artificial reaction networks.
The Artificial Reaction Network (ARN) is a bio-inspired connectionist paradigm based on the emerging field of Cellular Intelligence. It has properties in common with both AI and Systems Biology techniques including Artificial Neural Networks, Petri Nets, and S-Systems. In this paper, elements of temporal dynamics and pattern recognition are combined within a single ARN control system for a quadrupedal robot. The results show that the ARN has similar applicability to Artificial Neural Network models in robotic control tasks. In comparison to neural Central Pattern Generator models, the ARN can control gaits and offer reduced complexity. Furthermore, the results show that like spiky neural models, the ARN can combine pattern recognition and complex temporal control functionality in a single network
Drell-Yan diffraction: breakdown of QCD factorisation
We consider the diffractive Drell-Yan process in proton-(anti)proton
collisions at high energies in the color dipole approach. The calculations are
performed at forward rapidities of the leptonic pair. Effect of eikonalization
of the universal "bare"dipole-target elastic amplitude in the saturation regime
takes into account the principal part of the gap survival probability. We
present predictions for the total and differential cross sections of the single
diffractive lepton pair production at RHIC and LHC energies. We analyze
implications of the QCD factorisation breakdown in the diffractive Drell-Yan
process, which is caused by a specific interplay of the soft and hard
interactions, and resulting in rather unusual properties of the corresponding
observables.Comment: 19 pages, 7 figure
Azimuthal asymmetries in lepton-pair production at a fixed-target experiment using the LHC beams (AFTER)
A multi-purpose fixed-target experiment using the proton and lead-ion beams
of the LHC was recently proposed by Brodsky, Fleuret, Hadjidakis and Lansberg,
and here we concentrate our study on some issues related to the spin physics
part of this project (referred to as AFTER). We study the nucleon spin
structure through and processes with a fixed-target experiment using
the LHC proton beams, for the kinematical region with 7 TeV proton beams at the
energy in center-of-mass frame of two nucleons GeV. We calculate
and estimate the azimuthal asymmetries of unpolarized and
dilepton production processes in the Drell--Yan continuum region and at the
-pole. We also calculate the , and
azimuthal asymmetries of and dilepton production
processes with the target proton and deuteron longitudinally or transversally
polarized in the Drell--Yan continuum region and around resonances region.
We conclude that it is feasible to measure these azimuthal asymmetries,
consequently the three-dimensional or transverse momentum dependent parton
distribution functions (3dPDFs or TMDs), at this new AFTER facility.Comment: 15 pages, 40 figures. Version accepted for publication in EPJ
Modelling generalized parton distributions to describe deeply virtual Compton scattering data
We present a new model for generalized parton distributions (GPDs), based on
the aligned jet model, which successfully describes the deeply virtual Compton
scattering (DVCS) data from H1, ZEUS, HERMES and CLAS. We also present an
easily implementable and flexible algorithm for their construction. This new
model is necessary since the most widely used models for GPDs, which are based
on factorized double distributions, cannot, in their current form, describe the
DVCS data when employed in a full QCD analysis. We demonstrate explicitly the
reason for the shortcoming in the data description. We also highlight several
non-perturbative input parameters which could be used to tune the GPDs, and the
-dependence, to the DVCS data using a fitting procedure.Comment: 12 pages, 12 figures, revtex4, shortened version accepted for
publication in PRD, figures improved and references adde
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